1. Field of the Invention
The present invention generally relates to a digital video camera having automatic white balance and a method thereof. More specifically, the present invention relates to a digital video camera capable of performing automatic white balance adjustment according to the photographing condition such as whether it is indoor or outdoor, and determining the photographing condition at different speeds on the basis of the status of an iris.
2. Description of the Related Art
Technical advances in the electronics industry have brought the development of many types of cameras having diverse functions. Cameras now have automatic exposure and automatic white balance features. In automatic exposure or auto-iris mode, the lighting condition is measured by means of an exposure meter to automatically control an iris for ultimately creating an optimal exposure setting for the film condition.
In automatic white balance mode, the difference between the red component and the blue component comprised in the light from a light source is detected, and weights of red and blue are compensated, respectively, in a camcorder for maintaining color balance.
Meanwhile, although an object may be photographed by the exactly same camera, the color(s) of the photographed image can be different depending on lighting conditions. This is because most light sources have a certain color temperature expressed in Kelvin (K). The color temperature indicates light quality of a light source on the basis of the electromagnetic wave emitted from the light. To give averages of color temperature of conventional light sources, a bright midday sun is in range of 5,500-6,000K, a lightly overcast sky 6,000-7,000K, a fluorescent lamp 3,200-3,600K, and a candle 1,800-2,000K. Therefore, to perform white balance adjustment through the camera having an automatic white balance feature, the first thing to be done is finding out the type of a light source, that is, whether it is natural sunlight or artificial light.
FIG. 1 is a flow chart illustrating white balance adjustment of a conventional digital video camera having automatic exposure and automatic white balance. Referring to FIG. 1, first, the digital video camera checks a hall value corresponding to the current status of an iris that has been automatically determined according to the automatic exposure feature of the camera at S10. When a hall sensor outputs a voltage of a certain magnitude corresponding to the openness of the iris, the output voltage is then converted to digital or numeric value. This digital value is a hall value.
Next, the hall value is compared with a predetermined threshold value at step S20. At this time, the threshold value can be empirically determined.
In an outdoor place where natural sunlight is present, the iris is opened just a little so the hall value is small. On the other hand, in an indoor place where artificial light is present, the iris is opened fully so the hall value is large.
Therefore, if the hall value turns out to be equal to or greater than the threshold value the camera determines that it is an indoor place at step S30, but if the hall value is less than the threshold value the camera determines that it is an outdoor place at step S40.
On the basis of the determination result, the camera performs white balance adjustment at step S50. The white balance adjustment is different whether it is indoor or outdoor.
However, in a conventional digital video camera, white balance adjustment is so sensitive to even tiny changes of the hall value especially when the hall value and the threshold value are approximate. In such case, color sensitivity of a photographed image also changes very subtly. For instance, the hall value in a cloudy evening is usually very close to the threshold value. If a user zooms in to photograph an object with low color sensitivity, the hall value will be changed but subtly during the zoom process. Since the white balance adjustment gets changed continuously in correspondence to the changes in the hall value, the user often finds it very difficult to record moving images having stable color sensitivity.